The most common side effects of Prilosec are diarrhea, nausea, vomiting, headaches, rash and dizziness. Nervousness, abnormal heartbeat, muscle pain, weakness, leg cramps, and water retention occur infrequently. Call your doctor if you have any of these symptoms of low magnesium: Dizziness, confusion, Fast or uneven heart rate, Jerking muscle movements, Feeling jittery, Muscle cramps, muscle weakness or limp feeling, Cough or choking feeling, Seizure (convulsions) Inform with your doctor immediately if you experience unusual stomach pain. Contact your doctor immediately if you experience mental or mood changes (such as depression or agitation), chest pain, or fast or irregular heartbeat. Allergic reactions to this medicine are unlikely but seek immediate medical attention if it occurs. Symptoms of an allergic reaction include rash, itching, swelling, severe dizziness, or trouble breathing. High doses and long-term use (1 year or longer) may increase the risk of osteoporosis-related fractures of the hip, wrist, or spine. Therefore, it is important to use the lowest doses and shortest duration of treatment necessary for the condition being treated. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about additional side effects that you may experience.